Electron beam-intercepting structure for color image-producing cathode ray tubes



Unite States 3,102,967 ELECTRON BEAM-INTERCEPTING STRUCTURE FOR CLURlMAGE-PRODQING CATHDE RAY TUBES Louis R. Focht, Elkins Parli, Pa.,assigner, by mesne assignments, to Philco Corporation, Philadelphia,Pa., a corporation of Delaware Filed June 3, 1969, Ser. No. 33,769 i 8Claims. (Cl. 313-92) This invention relates to color image-producingcathode ray tubes of the index type wherein the color image is producedby successive and repetitive electron beam scanning of elements emissiveof light of different primary colors, such 'as red, green and blue, andwherein an index signal is also produced which is utilized to eifectcoordination between instantaneous beam modulation and beam position,such coordination being essential 'for proper color rendition. Suchcathode ray tubes are now well known. They are useful, for example, incolor television receivers. This invention relates to beam-interceptingstructures or screens for such cathode ray tubes.

The beam-intercepting structure of a tube of this type preferablycomprises phosphor stripes in successive triplets which extendtransversely to the direction of line scanning motion of the electronbeam, the stripes of each triplet being successively emissive of lightof different colors as the beam traverses them. The color writingfrequency is the nominal rate at which the writing beam traverses thecolor triplets, i.e. the number of triplets traversed per second. By=Way of example, this frequency may be 6 mc.

The index signal is produced by electron beam impingement of indexelements which vmay also be in the form of stripes extendingtransversely to the direction of line scanning. They may be composed ofa iluorescent material, such as zinc oxide, having a spectral output inthe non-visible light region, and the index signal may be derived `froma suitable photoelectric cell arranged, `for example, in a side wallportion of the cathode ray tube out of the path of the electron beam andfacing the beam-intercepting structure. Alternatively, the index signalmay be produced by secondary electron emission as Well understood in theart.

In operation of certain color image-producing cathode ray tubes of thetype here involved, the index elements tend to cause product-ion of anundesirable visible pattern in the color image. For example, with acertain desirable form of the beam-intercepting structure as hereinafterdescribed, the index elements necessarily overlap or shadow certain ofthe color elements and tend to cause production of an undesirablevisible pattern.

The principal object of the present invention is to provide an improvedbeam-intercepting str-ucture, the beam scanning of which does notproduce a visible pattern in the color image.

Another object of the invention is to provide a highly eicientbeam-intercepting structure.

Other objects `and features of the invention will be apparent .from thedescription to follow.

In one form of beam-intercepting structure according to this invention,the structure is caused to be non-productive of the yundesirable visiblepattern in the color image by a combination of dimensioning of theshadowed elements and adding other shadowing elements. ln another formof beam-intercepting structure 'according to this invention, thestructure is caused to be non-productive of the undesirable visiblepattern simply by dimensioninfg of the shadowed elements.

The invention may be fully understood from the following detaileddescription with reference to the accompanying drawing wherein:

3,102,967 Patented Sept. 3, 1963 FIG. l is a greatly enlargedfragmentary sectional plan View of a beam-intercepting structure of adesirable form in which, however, the index elements cause production ofthe aforementioned undesirable visible pattern in the color image;

FIG. 2 is a similar yiew of `a beam-intercepting structure of the samegeneral -form but embodying one form of this invention; and

FIG. 3 is a similar view of a beam-intercepting structure embodyinganother form of this invention.

Referring rst to FlG. l, the beam-intercepting structure there showncomprises a transparent substrate 1t) on which the color phosphorstripes are deposited. The substrate 19 may be the faceplate of thecathode ray tube or it may be a transparent member in proximity to thefaceplate. Red light-emissive phosphor stripes are shown at 1l; greenlight-emissive phosphor stripes are shown at 12; Iand bluelight-emissive phosphor stripes are shown at 13. Since the redlight-emissive phosphor is less eilicient than the green light-emissiveand blue light-emissive phosphors, the stripes 11 are made wider thanthe stripes 12 and 13 in order to achieve white balance. On the `rear ofthe color phosphor stri-pes there is provided a conventionalelectron-permeable and light-reilecting layerV 1li. This layer, whichmay be composed of laluminum for example, increases the brightness ofthe image by rellecting toward the observer those rays of light emittedfrom the rear of the color phosphor stripes in response to impingementof the electron beam thereon. The index stripes 15 are deposited on thelayer la, `and the latter also serves to separate the index stripes fromthe image-producing stripes.

ln a beam-intercepting structure of this character, it is desired tohave the index stripes l5 disposed behind alternate spaces between thecolor phosphor stripes. This is intended to serve twopurposes-namely,(a) to produce an index signal having a frequency 3/2)c where is thecolor writing frequency as explained above, and (b) to avoid shadowingof the color phosphor stripes by the index stripes. With respect to theproduction of a 3/21, i.e. 9 mc., index signal, this is a so-calledambiguous signal which is converted to a signal having the frequency f.There is no need to explain here the reason for the production of the3/2]c signal. For an explanation of this, reference may be had. to thecopending application of F. P. Keiper et al., Serial No. 797,684, filedMarch `6, 1959, assigned to the assignee of the present application.With respect to shadowing of the color phosphor stripes, if any of theindex stripes are disposed behind or overlap any of the color phosphorstripes, they (the index stripes) decrease the electron irnpingement onthe overlapped or shadowed color phos-l phor stripes and hence decreasethe light-emission of the stripes. While this is undesirable, itnecessarily results from the widening of the red light-emissive stripes11, as may be seen in FIG. 1, which will now be explained.

The distance between the center lines of two consecutive redlight-emissive stripes represents one cycle of color Writing, or 360color degrees. Thus the distance d1 represents one cycle and thedistance d2 represents the next cycle. Since this spacingof the redlight-emissive stripes must be maintained to maintain the proper colorwriting frequency, increasing the width of the red light-emssive stripesnecessarily decreases the width of the spaces between each of thosestripes and the adjacent blue and green light-emissive stripes,resulting in overlapping or shadowing of the red light-emissive stripesby some of the index stripes. This reduces the light output of the redlight-emissive stripes `and causes production of an undesirable visiblepattern in the color image as will now be explained.

becomes Visible to the human eye.

' duction of the index signal.

First it should be noted that at the color writing frequency, 6 mc.,lthe resolution ability of the human eye is inadequate for `discernmentof a pattern in the color image, but at substantially lower frequenciesa pattern In the screen structure of FiG. 1, the cycle d1 isrepresentative of alternate color cycles and the cycle d2 isrepresentative of the other alternate color cycles. That is to say, thecolor cycle following d2 is the same las d1, the next color cycle is thesame as d2, and so on. vAs the beam traverses the d1 color cycles itdoes not encounter any shadowed areas, but as it traverses the d2 colorcycles it encounters shadowed areas of the red light-emissive stripes.Thus in alternate color cycles the emitted red light output of thescreen is lower than it is in the other alternate color cycles, and thisproduces a pattern at one-half the color writing lfrequency, i.e. 3 mc.,which is within lthe resolution capability of the human eye and whichappearsas Y a coarse-line structure in the color image.

Referring now to FIG. 2, there is shown a beam-intercepting structure orscreen according to one embodiment of the present invention. Thisstructure is generally of the form of that of FIG. 1 but it embodiesfeatures according to this invention. The elements corresponding tothose of FIG. l are'designated by the same reference numerals with ytheaddition of the suix a.

In the structure of FIG. 2, the red light-emissive stripes 11a arewidened further on both sides to abut the adjacent blue and greenlight-emissive stripes, and additional stripes 16 are provided as shown.These stripes may have substantially the same electron transparency asthe index stripes 15a but they should not interfere With the pro- Eorexample, where the index stripes `are emissive of invisible light,stripes 16 y.should be composed of a material, such as an unactvatedphosphor, which will not emit light.

IIt will be seen that with this arrangement there are two shadowedportions of each red light-emissive stripe, and as the electron beamksweeps across the stripes 15a and 16, an invisible pattern at twice theindex frequency, i.e., 18 mc., is produced which, of course, is notobjectionable because -it is not seen. Moreover, even though the'redlight-emissive stripes are further shadowed, their light emission isactually greater than in the case of F'IG. 1 dueto their increasedWidth. It should be no-ted particularly that in this structure the lightoutput of the red light-emissive stripes is equalized in thesuccessive'color cycles. Therefore this screen structure does notproduce the undesirable visible pattern which is characteristic of thestructure of'FIG. 1.

Referring now to FIG. 3, there is shown a beam-intercepting structureaccording to another embodiment of this invention. 'Ihis structure 'isalso generally similar to that of FIG. 1 and the elements are designatedby the 'same reference numerals with` the sux b added. In this instance,the red light-emissive stripes 11b vare Widened in the areas adjacentthe index stripes. While the added portion of each red phosphor stripeis shadowed, the light output is increased. For example, suppose thatthe index stripes are 50 percent transmissive of electrons. In FIG. 1each index stripe covers 30 color degrees of the red phosphor, which isas if 15 color degrees had been removed.v In FIG. 3 this is counteractedby adding 30 color degrees of red phosphor adjacent each index stripe.

Thus in FIG. 3 the light output of the red light-emissive stripes isuniform in the successive color cycles. That is' to say, it is the samein the d2 color cycles as it is in the d1 rcolor cycles. Therefore asthe electron beam scans the screen there is no undesirable visiblepattern as in the case of FIG. 1.

It will be seen from the foregoing description that this inventionprovides a screen which is non-productive of an undesirable visiblepattern by equalizing the light output of the shadowed elements insuccessive color cycles.

While certain embodiments of the invention have been i illustrated anddescribed, it will be understood that the invention is not limitedthereto but contemplates such modifications and further embodiments asmay occur to those skilled in the I claim:

l. A color image-producing screen having colored lightemissive elementswhich are scanned by an electron beam in successive color cycles at apredetermined color writing frequency and also having index elements atleast some of which overlap portions of yelements emissive of light of aparticular color and tend to produce fa visible pattern at a frequencylower than said writing frequenc said screen being characterized bystructure for causing the light `output of the latter elements to besubstantially uniform or equal in the successive color cycles so thatlno undesirablevisible pattern is produced in the color image by virtue:of the shadowing effect of the overlapping index elements.

2. A color image-producing screen according to claim l, wherein theindex elements are adjacent to and coextensive with portions of saidelements emissive of light of aV particular color.

3. A color image-producing screen according to claim 2, whereinadditional elements are provided on the screen at least some `of whichoverlap portions of said elements emissive .of light of a particularcolor, said additional elements having substantially the same electrontransparency as said index elements and serving to prevent production ofan undesirable visible pattern in the color image.

4. A colorr image-producing screen having colored light-emissive stripeswhich are scanned transversely by an electron bearn in successive colorcycles alt a predetermined color writing frequency and also having indexstripes which in alternate color cycles overlap portions of stripesemissive of light ot a particular color and tend to produce a visiblepattern at one-half the writing frequency, said screen beingcharacterized by structure for causing the light output of the latterstripes to be substantially uniform or equal in the successive colorcycles so that no` undesirable visibile pattern is produced in the colorimage by virtue of the shadowing effect of the overlapping index stripesin alternate color cycles.

5. A color image-producing screen acconding to claim 4, wherein saidstripes emissive of light of a particular stripes having substantiallythe same electron transparency as said index stripes and serving toprevent production of: an undesirable visible pattern in the colorimage.

8. An electron beam-intercepting structure for a color` image-producingcathode `ray tube, comprising a transparent substrate, stripes supportedby said substrate which are successively and rrepetitively emissive Ioflight of different colors` in response to electron beam impingement, thestripes emissive of light of one color being wider than the otherstripes, light-emissive index stripes each adjacent to and coextensivewith a portion of one of said wider stripes, and other stripes notemissive of light each adjacent to and coextensive with another portionof `one of said wider stripes, said other stripes having sub-vstantially the same electron transparency as said index stripes.

References Cited in the le of this patent 6 Bradley J'uly 7, 1953Bradley 1 Sept. 14, 1954 Jesty Aug. 13, 1957 Clapp Aug. 11, 1959 `GrahamJuly 12, 1960

1. A COLOR IMAGE-PRODUCING SCREEN HAVING COLORED LIGHTEMISSIVE ELEMENTSWHICH ARE SCANNED BY AN ELECTRON BEAM IN SUCCESSIVE COLOR CYCLES AT APREDETERMINED COLOR WRITING FREQUENCY AND ALSO HAVING INDEX ELEMENTS ATLEAST SOME OF WHICH OVERLAP PORTIONS OF ELEMENTS EMISSIVE OF LIGHT OF APARTICULAR COLOR AND TEND TO PRODUCE A VISIBLE PATTERN AT A FREQUENCYLOWER THAN SAID WRITING FREQUENCY,